Responses of soil nematode community structure to soil carbon changes due to different tillage and cover crop management practices over a nine-year period in Kanto,Japan

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha⁻¹ for upland rice, and 0 and 20 kg N ha⁻¹ for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure.     

Organic and inorganic phosphorus in Mollisol soil under different tillage practices

The distribution of soil phosphorus (P) between different organic and inorganic forms depends on, among other factors, the tillage systems. The evaluation of soil P fractions is essential to determine if they are related to available P. The objective was to characterize the P forms from a soil under no tillage (NT) and conventional tillage (CT). Soil samples were taken at 0–5, 5–10 and 10–20 cm depth from a fine, mixed, thermic Petrocalcic Paleoudoll, after 8 years under NT and CT. Inorganic and organic P was measured in the anion exchange membrane (AEM), NaHCO₃, NaOH, NaOH after sonication, HCl and residual fractions extracted sequentially. Microbial P was determined by fumigating with chloroform after P extraction with AEM. The tillage systems did not affect the total P content but the distribution of P among fractions changed between NT and CT. No tillage system had significantly higher microbial P at all soil depths and ranged from 34 mg P kg⁻¹ at 0–5 cm to 10 mg P kg⁻¹ at 10–20 cm. In the upper 10 cm of soil, NT tended to have higher AEM-Pi and NaHCO₃-Pi comparing to CT system. The increase in AEM-Pi was closely related to organic carbon increases and pH decreases. The was a consistently higher concentration of NaOH-Po but the increase was significant al 5–10 and 10–20 cm, and represented on average about 35% of total P. The residual P which was considered mostly organic was also an important pool in both NT and CT, and accounted for about 30% of total P. Therefore, P availability is mainly controlled by organic P which makes up a larger proportion of total P.     

Changes in soil chemical characteristics with different tillage practices in a semi-arid environment

We examined the effects of various tillage intensities: no-tillage (NT), minimum tillage with chisel plow (MT), conventional tillage with mouldboard plow (CT), and zone-tillage subsoiling with a paraplow (ZT) applied in alternate years in rotation with NT, on the topsoil profile distribution (0–30 cm) of pH, soil organic carbon (SOC), organic N and available nutrients on a semi-arid soil from Central Spain. The equivalent depth approach was used to compare SOC, N and nutrient stocks in the various tillage treatments. Measurements made at the end of 5 years showed that in the 0–30 cm depth, SOC and N had increased under NT and ZT compared with MT and CT. Most dramatic changes occurred within the 0–5 cm depth where plots under NT and ZT had respectively 7.0 Mg ha⁻¹ and 6.2 Mg ha⁻¹ more SOC and 0.5 Mg ha⁻¹ and 0.3 Mg ha⁻¹ more N than under MT or CT. No-tillage and ZT plots, however, exhibited strong vertical gradients of SOC and N with concentrations decreasing from 0–5 to 20–30 cm. In the 0–20 cm layer, higher concentrations of P and K under NT and ZT than under MT or CT were also found. Soil pH under NT and ZT was 0.3 units lower than under MT or CT at a depth of 0–5 cm. This acidifying effect was restricted at the surface layer and in the 20–30 cm interval, pH values under NT and ZT were higher than in MT and CT plots. These results suggest that in the soil studied, ZT in rotation with NT maintain most advantages associated with NT, and present a definite potential for use as a partial-width rotational tillage practice.     

冷凉地区不同耕作措施对土壤环境和作物生长发育的影响

通过不同耕作措施的实施,比较其对玉米种植地土壤水分、土壤温度、玉米生长发育及产量的影响,从而探讨不同的耕作方式在旱作农业试验区的适宜性。结果表明:不同的保护性耕作措施均可提高土壤水分含量,其中留茬旋耕处理的土壤贮水量最高,达(4.542±0.894)×105L/hm2;在玉米播种前期及苗期,免耕覆盖处理降低土壤温度1~2℃,而整个生育期留茬旋耕处理与传统耕作处理的土壤温度相近;苗期,留茬旋耕处理的玉米株高、根长、鲜重和干重均优于其它处理,促进了玉米的生长发育;不同的保护性耕作措施均可提高玉米的产量,与传统耕作相比可增产4.01%~22.1%。整秆还田和留茬旋耕处理玉米产量较高,两者之间差异不显著。综合考虑不同耕作措施的效应,留茬旋耕处理比整秆还田处理更适宜于冷凉地区的推广、应用。     

水稻土厌氧氨氧化对不同耕作方式与秸秆还田的响应

【目的】研究稻田土壤厌氧氨氧化微生物活性、丰度和群落结构对不同耕作方式与秸秆还田的响应,为稻田土壤氮素管理提供科学依据。【方法】设置3个不同耕作方式(翻耕、旋耕、免耕)+秸秆还田处理,同时设置翻耕+秸秆不还田处理作为对照,采用_¹⁵N示踪法、荧光定量PCR及Illumina测序分别分析厌氧氨氧化菌潜在活性、功能基因hzsB拷贝数及群落组成。【结果】秸秆还田条件下,厌氧氨氧化菌潜在活性表现为免耕>旋耕>翻耕(p<0.05),对照与旋耕+秸秆还田处理无显著性差异。各处理之间厌氧氨氧化菌功能基因(hzsB)拷贝数无显著性差异。Illumina测序从属水平鉴定出Kuenenia和Scalindua两种已知的厌氧氨氧化菌及部分未鉴定属,且各处理间二者的相对丰度具有负相关关系(p<0.05)。相关性分析结果表明,厌氧氨氧化菌活性与土壤反硝化活性显著相关,与功能基因拷贝数及群落组成无显著相关性。【结论】水稻田长期秸秆还田和不同耕作方式改变了厌氧氨氧化菌活性和群落组成,但其数量未发生显著变化。水稻田秸秆还田加翻耕可一定程度上抑制土壤氮损失,而秸秆还田与免耕结合的田间管理方式提高了土壤氮素损失潜力。     

Soil tillage and cover crop on soil CO2 emissions from sugarcane fields

Soil tillage is an agricultural practice that directly affects the global carbon cycle. Our study sought to assess the implications of adopting sunn hemp cover crops with different tillage practices on CO₂ emissions for two soil types (clayey and sandy soil) cultivated with sugarcane in Brazil. The experimental design was a split‐plot with randomized blocks, with the main plots being with cover crop or fallow and sub‐plots being under conventional or minimum tillage. Our results indicate that during the first 50 days after soil tillage, the variation in soil CO₂ emissions was stimulated by cover crop and soil tillage, while after that, it became dominated by the root respiration of sugarcane plants. We also found that over the first 97 days after the tillage, the clayey soil showed differences between minimum tillage with cover crop and fallow. Conversely, for sandy soil over the first 50 days following, there were differences between the tillage systems under cover cropping. Emissions from sugarcane rows were found to be greater than those from inter‐row positions. We concluded that soils under different textural classes had distinct patterns in terms of soil CO₂ emissions. The correct quantification of CO₂ emissions during the sugarcane renovation period should prioritize having a short assessment period (~50 days after soil tillage) as well as including measurements at row and inter‐row positions.     

Weed growth and crop yield responses to tillage and mulching under different crop rotation sequences in semi‐arid conditions

Conservation agriculture (CA) is thought to reduce weed pressure from the third year of adoption, when recommended practices are followed. Weed growth and crop yield were assessed during the third and fourth year of maize–cowpea–sorghum rotation, second and third year of maize–cowpea rotation and first and second year of maize monocropping on a clay loam soil at Matopos Research Station (annual rainfall, 573 mm) following recommended CA management practices. Each experiment had a split‐plot randomized complete block design with mouldboard plough (CONV), minimum tillage (MT) with ripper tine and planting basins as main‐plot factor and maize residue mulch rate (0, 2 and 4 t/ha) as a subplot factor, with threefold replication. All subplots were surface mulched and weeded by hoe at the same time. We hypothesized that under MT weed growth would be considerable with maize monocropping but from year 3 of CA, weed growth would decrease and crop yield increase relative to values from unmulched CONV. Minimum tillage increased weed growth in 2nd year of maize monocropping. Under the maize–cowpea rotation, the considerable weed growth in planting basins was likely due to the large intrarow spacing and poor light competiveness of the cowpea variety. Mulch contributed to weed growth being suppressed by up to 36% under CA in the maize–cowpea–sorghum rotation relative to unmulched CONV. When planted on the same date, crop yield did not differ between CA and unmulched CONV. Maize–cowpea–sorghum rotation grain yield (3143 kg/ha) was double that under monocropping , probably due to improvements in soil physical and chemical conditions.     

Soil tillage and crop productivity on a Vertisol in Ethiopian highlands

Soil quality deterioration and consequent reduced productivity characterize the Vertisols in the highlands of Ethiopia. The problem is exacerbated by lack of appropriate land preparation alternatives for the major crops in the area. A field experiment was carried out for 6 years (1998–2003) at Caffee Doonsa in the central highlands of Ethiopia to evaluate alternative land preparation methods on the performance of wheat (Triticum durum Desf.), lentil (Lens culinaries Medik L) and tef (Eragrostis tef L) grown in rotation. Four methods of land preparation (broad bed and furrow, green manure, ridge and furrow and reduced tillage) were arranged in a randomized complete block design with three replications on permanent plots of 22 m by 6 m. Broad bed and furrow significantly increased the grain yield of lentils by 59% (from 1029 to 1632 kg ha⁻¹) as compared to the control. On the other hand, reduced tillage resulted in the highest grain yield of wheat (1862 kg ha⁻¹) and tef (1378 kg ha⁻¹) as compared to 1698 kg ha⁻¹ of wheat and 1274 kg ha⁻¹ of tef for the control although the increase was not statistically significant. A gross margin analysis showed that BBF is the most profitable option for lentil with 65% increase in total gross margin. On the other hand, RT resulted in 11 and 8% increase in gross margin of wheat and tef, respectively as compared to the control. Based on the agronomic and economic performances best combinations of crop and land preparation method were: lentil sown on broad bed and furrow, and wheat and tef sown after reduced tillage.     

Phosphorus losses from a structured clay soil in relation to tillage practices

Abstract. Preferential flow may enhance phosphorus transport through the soil profile and thereby increase the risks for eutrophication of watercourses. Destruction of continuous macropores in topsoil by tillage provides the possibility for better contact between soil particles and P fertilizer. This is facilitated by incorporation rather than surface application of fertilizer, which should reduce the risk of rapid P transport from the soil surface through the unsaturated zone. To test this hypothesis, undisturbed soil monoliths (0.295 m in diameter and 1.2 m in length) were collected at a field site with a clay soil in which preferential flow is the dominant solute transport mechanism. After three years of observation, average total P loads reached 1.86, 1.59 and 1.25 kg ha^–1for no-tillage, conventional tillage, and conventional tillage where the P fertilizer was incorporated, respectively. More than 80% of total losses were in the form of dissolved P. The tillage treatment had no significant effect on P leaching loads compared to no-tillage, but the improved contact between soil particles and P fertilizer resulting from fertilizer incorporation significantly reduced P loads during the first year after application of 100 kg P ha^–1. However, after further application of 100 kg P ha^–1 two years later, there were no significant differences between the treatments.     

不同施肥和耕作制度下土壤微生物多样性研究进展

本文主要介绍了运用Biolog GN、磷脂脂肪酸(PLFA)、核酸分析法进行土壤微生物群落分析的优缺点,综述了施肥、耕作两种农业措施对土壤微生物多样性影响的研究进展。指出不同施肥处理对微生物影响效果不同,合理施用有机肥有利于维持土壤微生物的多样性及活性;由于受其他环境因素(如土壤类型、农作制度、残茬量等)的影响,不同耕作措施对土壤微生物多样性影响有差异,但是大多试验结果显示免耕、少耕能增加微生物多样性和生物量,保持系统的稳定性。文章还指出了目前研究中存在的问题,并对今后的研究方向做了展望。     

草甸黑土团聚体稳定性对耕作与炭基肥施用的响应

为了阐明东北草甸黑土典型区域短期耕作深度及炭基肥料施入对土壤团聚体稳定性影响,2016－2018年连续3 a翻耕秸秆全量还田玉米地上,设置深耕（DCF）与旋耕(SCF),配施有机肥(M)和生物炭(C),共6个处理：DCF、DCF+M、DCF+B、SCF、SCF+M、SCF+B。利用干湿筛法获得土壤团聚体6个粒级组,分析了平均重量直径（mean weight diameter,MWD）、水稳性团聚体比例（water-stable aggregate,WSA）、团聚体破坏度（percentage of aggregate destruction,PAD）、水稳性团聚体几何直径（geometric mean diameter,GMD）以及土壤团聚体有机碳组成和游离结晶态铁铝氧化物（FeDCB和AlDCB）、无定性态铁铝氧化物（Feoxa和Aloxa）。结果表明,耕作方式和施肥显著影响土壤团聚体组成,影响程度表现为旋耕＞深耕,增施有机肥＞常规施肥＞增施生物炭。不同形态铁铝氧化物质量分数在0.10～2.45 g/kg之间,游离结晶态铁铝氧化物含量显著高于无定形态铁铝氧化物含量。除FeDCB外,DCF处理铁铝氧化物含量均高于DCF+B处理,SCF处理Aloxa含量显著高于SCF+M、SCF+B处理19.35%和12.12%; Feoxa和Aloxa与>0.25 mm团聚体、WSA相关性大于其他影响因素,Feoxa对变异解释贡献率为61.3%。土壤有机碳含量与<0.25 mm团聚体负相关,而与>0.25 mm团聚体成正相关,其贡献率为33.0%。AlDCB、Aloxa及>0.25 mm团聚体的形成呈正相关关系,二者总贡献率为9.3%;铁铝氧化物及有机碳改变共同解释74.9%土壤团聚体稳定性和粒级分布,铁铝氧化物单独贡献率为7.9%,有机碳组分单独贡献率为9.2%;综上所述,短期耕作与炭基肥料施入对土壤结构稳定性影响显著,SCF+M是比较理想的耕作模式,在草甸黑土改良中具有一定应用价值。     

Soil fungal population in preharvest maize ecosystem in different tillage practices in Argentina

The distribution of the soil borne fungal population in maize non-rhizospheric soil in experimental trials were studied during the harvest seasons 2000/2001 and 2001/2002. The effect of different tillage practices was evaluated. Soil samples were collected from three tillage treatments, conventional tillage, reduced tillage and no tillage, with and without grazing. The distribution of fungal propagules in different treatments was compared. Soil samples were collected from the top soil (3 cm) before planting, in the sprong. No tillage without grazing and reduced tillage with grazing had the highest densities of filamentous fungi (5.71 and 5.85 log, respectively). The mycological survey showed the presence of six genera of filamentous fungi. They were Aspergillus, Fusarium, Penicillium, Trichoderma, Cladosporium, Alternaria. The species identified from genus Aspergillus were A. flavus, A. restrictus, A. candidus, A. parasiticus and other Aspergillus spp. The species identified from genus Penicillium were P. pinophylum, P. citreonigrum, P. implicatum, P. purpurogenum, P. minioluteum, P. waksmanii, P. restrictum, P. rugulosum, P. funiculosum and P. variabile. Species from genus Fusarium were identified as F. verticillioides, F. oxysporum, F. proliferatum and others Fusarium species. The isolation frequency of Aspergillus increased in the no tillage and grazing practices treatments. The data indicate that different agricultural practices impact soil inocula of principal maize toxigenic fungi in the production area. To our knowledge, this is the first report on the effect of tillage management practices on fungal populations in preharvest maize agroecosystem in Argentina.     

Soil carbon fractions and relationship to soil quality under different tillage and stubble management

Effect of 19 years of different tillage (direct drilled vs. conventional tillage) and stubble management (stubble retained vs. burnt) on soil carbon fractions were studied in a red earth, an Oxic Paleustalf at Wagga Wagga, NSW. The changes in carbon fractions were related to observed changes in soil structural stability and nitrogen availability. Significant differences in total organic carbon (TOC) were detected to 0.20 m depth, but the largest differences existed in the top 0.05 m where a difference of 8.0 g/kg (equivalent to 5.2 t ha⁻¹) was found between the extreme treatments (direct drilled/stubble retained (DD/SR) vs. conventional cultivation/stubble burnt (CC/SB)). Tillage had a much greater effect in reducing total carbon than stubble burning accounting for 80% of the total difference between the extreme treatments in 0–0.05 m layer. Tillage and stubble burning resulted in lower levels of different organic carbon fractions with tillage preferentially reducing the particulate organic carbon (POC) (>53 μm) (both free and associated POCs), whereas stubble burning reduced the incorporated organic carbon (<53 μm). We also found that tillage and stubble burning both significantly lowered the water stability of aggregate >2 mm, whereas stubble burning was related to the reduction of water stability of aggregates <50 μm. Furthermore, tillage was related to the decline in mineralisable nitrogen (MN) due to the loss of POC, especially the free POC fraction. POC was a more sensitive indicator of soil quality changes under different tillage and stubble management than TOC.     

Developing disease-suppressive soils through crop rotation and tillage management practices

A field laboratory was established in Prince Edward Island, Canada, to determine the effects of 2- and 3-year crop rotations, with conventional and minimum tillage treatments, on the severity of soilborne diseases of potato. The 2-year rotation consisted of spring barley and potato (cv. ‘Russet Burbank’), and the 3-year rotation was barley (undersown with red clover), red clover and potato. Examination of potato stem, stolon, and tuber tissues revealed significantly (P=0.05) lower levels of canker and black scurf caused by Rhizoctonia solani, in plants grown in 3-year vs. 2-year rotations. The severity of dry rot (Fusarium spp.) and silver scurf (Helminthosporium solani) was significantly (P=0.05) lower in tubers from plots managed with 3-year rotations and minimum tillage practices. Potato tubers harvested from 3-year rotational soils were significantly (P=0.05) less diseased than those from 2-year rotational soils following inoculation with Phytophthora erythroseptica, causal agent of pink rot. In greenhouse experiments using field soils from 2- and 3-year rotations, we found that potato plants growing in 3-year rotational soils were significantly (P=0.05) less diseased than those growing in 2-year rotational soils following inoculation with P. erythroseptica. Analysis of root zone bacteria recovered from the rhizosphere (exoroot) and potato root tissues (endoroot) showed that the greatest antibiosis activity inhibiting the growth of soilborne pathogens in vitro occurred in bacterial isolates recovered from the endoroot tissues of 3-year rotation crops under minimum tillage management. Our evidence supports the view that soil agroecosystems can be modified through rotation and conservation tillage practices to improve disease suppression by enhancing the antibiosis abilities of endophytic and root zone bacteria (endo- and exoroot).     

Soil CO2 emission and its relationship to soil properties under different tillage systems

There is a lack of understanding as to which soil property is the most important at regulating the temporal variability of soil CO₂ emissions on China’s Loess Plateau. The objective of this study was to evaluate the CO₂ emissions and their relationships to certain soil properties in a winter wheat (Triticum aestivum L.) field subject to no-till (NT) and conventional tillage (CT) practices. The CO₂ emissions were signi?cantly higher in the CT (257.6 mg CO₂ m^?2 h^?1), compared with the NT (143.8 mg CO₂ m^?2 h^?1), treatment. Soil organic matter content and carbon stock were 8% and 14% higher, respectively, in the NT, compared with the CT, treatment. Regression analyses between the CO₂ emissions and soil properties, including soil temperature and carbon stock, explained up to 88% and 60% of the temporal variability in CO₂ emissions in the NT and CT treatments, respectively. Linear correlations between the soil temperature and CO₂ emissions were recorded in both the NT and CT treatments. Soil temperature was the most important factor in terms of understanding the temporal variability in CO₂ emissions in wheat fields of the study area.     

Soil tillage for crop production and for protection of soil and environmental quality: a Scandinavian viewpoint

Based on experience from 35 years of tillage research in Sweden, future development of soil tillage is discussed and some research problems are identified. Tillage and seeding methods must be more carefully adapted to conditions at individual sites and occasions. Low-pressure typres, better weed control and improved seed coulters favour the increased use of reduced tillage. In order to diminish the impact of agriculture on the environment, it is necessary to develop methods for establishment of crops in the early spring or immediately after harvest, even in soils with large amounts of crop residues or high moisture content. The roles of tillage methods, and of soil compaction and structure on environmental impact of agriculture must be investigated. World food production must increase, since the world population is rapidly increasing. Therefore, it is necessary to develop improved crop production systems, including crop establishment systems, which favour efficient use of basic crop growth factors, while protecting or increasing soil productivity. Compaction, decreased organic matter content, and erosion are important long-term threats to soil productivity.     

Water management in various crop production systems related to soil tillage

Soil tillage, of different types and intensity and performed at different antecedent soil moisture conditions, is an important tool for agricultural water management. Tillage systems have important applications for increasing irrigation efficiency, enhancing the effectiveness of drainage systems, improving water quality, decreasing runoff losses and minimizing soil erosion, increasing runoff losses for water harvesting and supplemental irrigation, and decreasing percolation losses and creating aquatic environments for rice cultivation. The versatility and diversity of applications of tillage systems depend on the choice of tillage techniques. No-tillage methods with residue mulches are useful to conserve soil water. Chisel tillage and subsoiling methods along with ridge-tillage techniques are useful in increasing irrigation efficiency. No-tillage systems are useful in decreasing sediment density and transport of sediment laden pollutants in runoff, and puddling and wet tillage techniques or soil compaction are used in rice cultivation. Finally soil compaction and techniques to increase water repellence are useful for water harvesting for subsequent use in supplemental irrigation.     

Dynamics of soil biota at different depths under two contrasting tillage practices

One aim of conservation tillage is to preserve soil biological properties. This study was conducted to examine the effects of two contrasting tillage treatments on soil biota at different depths. We investigated the population dynamics and vertical distributions of microbes and several soil faunal groups for 2 years in field Andosols in northeastern Japan. The experimental plots were under no tillage (NT) or conventional tillage (CT, rotary tilled to 20 cm) management. In the 0–10-cm soil layer, bacterial and fungal substrate-induced respiration (SIR) and the population density of enchytraeids were higher under NT than under CT, but the population densities of protozoa, mites, and collembolans did not differ significantly. In contrast, at 10–20 cm, both SIR values were higher under CT, where larger populations of mites and collembolans were recorded. At both depths, nematodes were more abundant under CT. Thus, the effects of tillage on these soil organisms differed according to soil depth, and negative impacts of tillage were smaller in the deeper layer. Larger amounts of earthworm casts at the soil surface in NT plots showed a greater biomass of earthworms than in CT. To evaluate the activities of soil biota, we buried litterbags with three different mesh sizes at the two depths and examined the rate of decomposition. The daily decay constant of litter in the surface soil layer (1.5–8.5 cm) was greater under NT. We suppose that the activities of soil biota in this layer were stimulated under NT, and that especially microbes and enchytraeids, which were abundant at 0–10 cm, contributed greatly to the decomposition.     

Weather and other environmental factors influencing crop responses to tillage and traffic

Historical research approaches to crop responses to tillage and traffic are discussed and the causes and nature of these responses are analyzed and schematized. The complex of interrelations is then reduced to the changes in soil structure which affect root growth. More attention should be given to modifications in pore geometry caused by compaction, deformation and natural regeneration, both on a macro- and a micro-scale. The possible effects of modifications in pore geometry on soil physical, chemical and biological properties are analyzed in detail, in relation to weather and other environmental factors.In quantifying the interrelationships, good progress has been made, but the integration of separate effects under specific field conditions has not been developed sufficiently. More attention is needed for evaluation of potential growth-limiting factors which can be modified by tillage and traffic.It is proposed to consider the water status of the soil as the central link in the interaction between relevant environmental factors and crop responses to tillage and field traffic.     

Use of simulation to assess the effects of different tillage practices on land qualities of a sandy loam soil

Four different soil-structure types could reproducibly be recognized by soil surveyors working on Dutch sandy loam soils with different management practices. The 4 structure types were soils with a primary ploughpan, a loosened ploughpan, a secondary ploughpan and a grassland structure. These types had significantly different soil-physical properties and rooting depths. Soil-water regimes for a 30-year period were stimulated to obtain quantitative information on the influence of soil structure, as an expression of different soil-management practices, on land qualities such as moisture deficit, aeration status and workability.These land qualities were not significantly different for the 3 structure types of arable land when considering the entire soil profile. However, differences in moisture content and aeration status were significant when undisturbed and disturbed ploughpans were compared. Deep ploughing to disrupt the primary ploughpan should therefore not be encouraged in these soil as long as common field operations remain unchanged. The same land qualities for grassland indicated what may be attained by soil-structure regeneration. The probability of having a workable day in spring or autumn is increased by an estimated 20%, and the number of days with adequate aeration by 10%, in soil-structure types of arable land (A, B and C) as compared with grassland soil structure (D). Moisture deficits in the growing season should be about 50% less.In this study, simulation was not used to simulate soil-structure formation as a function of soil management, but soil structure was used as an input for the models, reflecting different management practices. To that end, the various structure types were characterized by physical measurements.